Members of the group flew on all of the NASA crewed orbital programs of the 20th century – Mercury, Gemini, Apollo, and the Space Shuttle. Gus Grissom died in 1967, in the Apollo 1 fire; the others all survived past retirement from service. Alan Shepard became the first American in space in 1961, and walked on the Moon on Apollo 14 in 1971. John Glenn became the first American in orbit in 1962, and went on to become a U.S. senator. He flew on the Shuttle in 1998 to become the oldest person to fly in space. He was the last living member of the Mercury Seven when he died in 2016 at the age of 95.

The STG next had to decide on a name for the people who would fly into space. A brainstorming session was held on December 1, 1958. By analogy with "aeronaut", someone came up with the term "astronaut", which meant "star traveller", although Project Mercury's ambitions were far more limited. They thought that they had coined a new word, but the term had been used in science fiction since the 1920s.[8] A three-man panel consisting of Charles J. Donlan, Warren J. North and Allen O. Gamble drew up a civil service job specification for astronauts. The panel proposed that astronauts be in civil service grades 12 to 15, depending on qualifications and experience, with annual salary of $8,330 to $12,770 (equivalent to $71,594 to $109,755 in 2018).[11] The panel described the duties of an astronaut:

Although the entire satellite operation will be possible, in the early phases, without the presence of man, the astronaut will play an important role during the flight. He will contribute by monitoring the cabin environment and by making necessary adjustments. He will have continuous displays of his position and attitude and other instrument readings, and will have the capability of operating the reaction controls, and of initiating the descent from orbit. He will contribute to the operation of the communications system. In addition, the astronaut will make research observations that cannot be made by instruments; these include physiological, astronomical and meteorological observations.[12]

Although the panel considered that many people might possess the required skills—aircraft pilots, submariners, deep sea divers and mountain climbers were all considered likely prospects—it decided that they could be best met by military test pilots.[13] Accepting only military test pilots would simplify the selection process, and would also satisfy security requirements, as the role would almost certainly involve the handling of classified information.[11] The decision to restrict selection to military test pilots was taken by Glennan, Dryden and Gilruth in the last week of December 1958, but the irony of using military test pilots in a civilian program was not overlooked, and in view of the President's express preference for a civil space program, Glennan thought it best to run the decision past Eisenhower. A meeting was arranged with the President, who was convinced by their arguments, and approval was given.[12][14]

The height limit was a function of the design of the Mercury spacecraft, which could not accommodate someone taller.[16] It was still uncertain as to whether piloting in the conventional sense would ever be possible in a spacecraft,[15] but from the beginning the spacecraft design provided for some degree of manual control.[17]

The first step in the selection process was to obtain the service records of graduates of test pilot schools from the United States Department of Defense. All services agreed to cooperate fully, and handed over their records. There were 508 military test pilots in total, of whom 225 were Air Force, 225 Navy, 23 Marine Corps and 35 Army. Donlan, North, Gamble and Robert B. Voas then went through the records in January 1959, and identified 110 pilots—five Marines, 47 from the Navy, and 58 from the Air Force—who met the rest of the minimum standards.[18] The 110 were then split into three groups, with the most promising in the first group.[19]

The candidates were given three briefings by NASA officials. The first was about NASA and Project Mercury; the second concerned the role of the pilot in the project; and the third was about the proposed astronaut training syllabus. In the afternoon candidates had short individual meetings with the NASA selection committee. It was emphasised that participation was entirely voluntary, that candidates were free to decline, and that there would be no career repercussions if they did so. Several candidates declined at this point.[22]

The rest reported to NASA Headquarters in Washington, DC, the following day for further screening. Voas gave them a series of standardized tests: the Miller Analogies Test to measure IQ; the Minnesota Engineering Analogies Test to measure engineering aptitude; and the Doppelt Mathematical Reasoning Test to measure mathematical aptitude. Donlan, North and Gamble conducted interviews in which they asked technical questions, and queried candidates about their motivations for applying to the program. Candidates were evaluated by two USAF psychiatrists, George E. Ruff and Edwin Z. Levy. A USAF flight surgeon, William S. Augerson, went over the candidates' medical records. Some were found to be over the height limit, and were eliminated at this juncture.[22]

The process was repeated with a second group of 34 candidates a week later. Of the 69, six were found to be over the height limit, 15 were eliminated for other reasons, and 16 declined. This left NASA with 32 candidates: 15 from the Navy, 15 from the Air Force and two from the Marine Corps.[23] Since this was more than expected, NASA decided not to bother with the remaining 41 candidates, as 32 candidates seemed a more than adequate number from which to select 12 astronauts as planned. The degree of interest also indicated that far fewer would drop out during training than anticipated, which would result in training astronauts who would not be required to fly Project Mercury missions. It was therefore decided to cut the number of astronauts selected to just six.[24][25]

All were male and white, as women were not yet accepted into the military test pilot schools,[33] and the first African-American to graduate from the USAF Experimental Test Pilot School, John L. Whitehead Jr.,[34] did so only in January 1958,[35] and was not one of the finalists.[32] Yet the Mercury Seven were similar beyond what was a simple result of the section criteria. Four were their fathers' namesakes.[20] All were the eldest or only sons in their families.[36] All were born in the United States,[33] and were raised in small towns. All were married with children, and all were Protestants.[20]

Shepard was the tallest, at the maximum height of 5 feet 11 inches (1.80 m); Grissom, the shortest at 5 feet 7 inches (1.70 m). Their ages at the time of selection ranged from 32 (Cooper) to 37 (Glenn). Cooper was also the lightest, at 150 pounds (68 kg), while Glenn was at the maximum weight of 180 pounds (82 kg), and Schirra was slightly overweight at 185 pounds (84 kg), and had to lose weight to be accepted. Both had to watch their weight carefully while they were in the space program.[37] IQs ranged from 135 to 147.[20]

Glenn and Carpenter did not meet all of their schools' degree requirements, including the completion of Glenn's senior year in residence and final proficiency exam, and Carpenter's final course in heat transfer. Although both were admitted on the basis of professional equivalency, Glenn had also completed additional coursework as a part-time student at the University of Maryland, College Park from 1956 to 1959. Both were ultimately awarded their bachelor's degrees after their 1962 space flights.[42][43]

Despite the extensive physical examinations, Slayton had an undiagnosed atrial fibrillation, which resulted in his grounding on the eve of what would have been his first space flight, and the second manned orbital mission.[44]

NASA introduced the astronauts in Washington, DC on April 9, 1959.[45] Although the agency viewed Project Mercury's purpose as an experiment to determine whether humans could survive space travel, the seven men immediately became national heroes and were compared by Time magazine to "Columbus, Magellan, Daniel Boone, and the Wright brothers."[20] Two hundred[20] reporters overflowed the room used for the announcement and alarmed the astronauts, who were unused to such a large audience.[46]

Because they wore civilian clothes, the audience did not see them as military test pilots but "mature, middle-class Americans, average in height and visage, family men all".[47]. To the astronauts' surprise, the reporters asked about their personal lives instead of war records or flight experience, or about the details of Mercury. After Glenn responded by speaking eloquently "on God, country, and family" the others followed his example,[47] and were applauded by the reporters.[20]

Born in Boulder, Colorado, Carpenter joined the U.S. Navy in 1949, and flew multi-engine Lockheed P-2 Neptune patrol aircraft. He graduated from the U.S. Naval Test Pilot School at NAS Patuxent River, Maryland, with Class 13 in 1954. Carpenter flew Mercury-Atlas 7, the second orbital Mercury mission. He took a leave of absence from NASA in the fall of 1963 to participate in the Navy's SEALAB program, and sustained an injury to his left arm in a motorbike accident. Two surgical interventions in 1964 and 1967 failed to correct the condition, and he resigned from NASA in August 1967, and from the Navy in 1969, with the rank of commander.

Born in Mitchell, Indiana, Grissom joined the USAF in 1950, and flew 100 combat missions in the Korean War as an F-86 Sabre pilot. He graduated from the USAF Experimental Flight Test School at Edwards Air Force Base, California, with class 56D (the same class as Gordon Cooper) in 1956. Grissom flew in space on Mercury-Redstone 4, the second suborbital Mercury flight, and then as Command Pilot of Gemini 3, the first manned Gemini mission in 1965, becoming the first person fly in space twice. He was designated as commander of Apollo 1 but was killed in a fire during a launch pad rehearsal test. At the time of his death, he was a lieutenant colonel in the USAF.

Born in Hackensack, New Jersey, Schirra graduated from the United States Naval Academy at Annapolis, Maryland, in 1945. After service afloat during World War II, he qualified as a pilot in 1948, and saw service on exchange with the USAF as a fighter pilot in the Korean War, flying 90 combat missions, and downing two MiGs. He qualified as a test pilot with class 20 at the U.S. Naval Test Pilot School in 1958. Schirra flew in space on Mercury-Atlas 8, the third orbital Mercury flight; on Gemini 6A in 1965; and Apollo 7, the first manned Apollo mission. Schirra was the first person to be launched into space three times, and the only one to fly Mercury, Gemini, and Apollo missions. He resigned from NASA and the U.S. Navy with the rank of captain in 1969, and joined CBS News as Walter Cronkite's co-anchor for the broadcasts of the Apollo Moon landing missions

Born in Derry, New Hampshire, Shepard graduated from the United States Naval Academy at Annapolis, Maryland, in 1944. After service afloat during World War II, he qualified as a pilot in 1947, and as a test pilot at the U.S. Naval Test Pilot School in 1950. Shepard flew in space on Mercury-Redstone 3, the first manned Mercury flight, and became the first American in space. He was slated to command the last Mercury flight, Mercury-Atlas 10, but it was cancelled, and then the first Project Gemini flight, but he was grounded in 1963 after being diagnosed with Ménière's disease, a condition in which fluid pressure builds up in the inner ear, resulting in disorientation, dizziness, and nausea. He stayed with the space program, accepting the position of Chief of the Astronaut Office, until an experimental corrective surgery cured him, and he was returned to flight status in May 1969. In 1971, he commanded Apollo 14, the third manned lunar landing mission, and became the fifth and oldest man to walk on the Moon. He was promoted to rear admiral, the first astronaut to reach this rank. He retired from NASA and the U.S. Navy in 1974.

The astronauts participated in Project Mercury's design and planning.[70] They divided the work between them. Carpenter had training in airborne electronics and celestial navigation, so he assumed responsibility for the spacecraft's communications and navigation systems. Grissom had a degree in mechanical engineering, so he became responsible for the attitude control systems. Glenn had experience flying many types of aircraft, so he oversaw the cockpit layout. Schirra drew responsibility for the life support systems and the pressure suits. Drawing on his experience as a Naval officer, Shepard looked after the tracking network and liaised with the Navy on recovery operations. Cooper and Slayton were Air Force officers with engineering backgrounds, so they dealt with the Redstone Arsenal and Convair, who built the Redstone and Atlas boosters used by Project Mercury.[71] The Mercury astronauts affected the design of the Mercury spacecraft in significant ways, insisting that a window be installed, and pressing for a greater degree of astronaut to autonomy in flying the spacecraft.[72]

The astronauts remained on active duty as military officers, and were paid according to their rank. To supplement their travel, they were provided a $9 per diem (equivalent to $77 in 2018) for day trips, and a $12 per diem (equivalent to $103 in 2018) for overnight trips, which did not cover the cost of hotels and restaurant meals. As a result, astronauts avoided spending money while traveling, as they were personally responsible for costs over their allotted per diem. An important component of their income was monthly flight pay, which ranged from $190 to $245 (equivalent to $1,633 to $2,106 in 2018).[73]
The astronauts traveled to meetings around the country on commercial flights, which forced them to continue earning their flight pay by flying aircraft on weekends. Grissom and Slayton regularly drove to Langley Air Force Base, and attempted to fly the required four hours a month, but had to compete for T-33 aircraft with colonels and generals. Cooper travelled to McGhee Tyson Air National Guard Base in Tennessee, where a friend let him fly higher-performance F-104B jets. This came up when Cooper had lunch with William Hines, a reporter for The Washington Star, and was duly reported in the paper. Cooper then discussed the issue with CongressmanJames G. Fulton. The matter was taken up by the House Committee on Science and Astronautics.[74][75] Within weeks the astronauts were given priority access to USAF T-33s, F-102s and F-106s at Langley. In 1962, NASA acquired a fleet of T-38s for their use.[76]

Plaque at Launch Complex 14

After General Motors executive Ed Cole presented Shepard with a brand-new Chevrolet Corvette, Jim Rathmann, a racing car driver who won the Indianapolis 500 in 1960, and was a Chevrolet dealer in Melbourne, Florida, convinced Cole to turn this into an ongoing marketing campaign. Henceforth, astronauts were able to lease brand-new Corvettes for a dollar a year. All of the Mercury Seven but Glenn took up the offer. Cooper, Grissom and Shepard were soon racing their Corvettes around Cape Canaveral, with the military and local police ignoring their exploits. From a marketing perspective, it was very successful, and helped the highly priced Corvette become established as a desirable brand.[77] The Mercury astronauts established the style and appearance of astronauts. "I soon learned", Gene Kranz later recalled, "if you saw someone wearing a short-sleeved Ban-Lon shirt and aviator sunglasses, you were looking at an astronaut."[78] While busy with the intense training for their flights,[79] they also drank and partied.[80] Some had affairs with the female astronaut groupies that flocked around them.[81] NASA actively sought to protect the astronauts and the agency from negative publicity and maintain an image of "clean-cut, all-American boy[s]."[82] The seven Mercury astronauts agreed to share equally any proceeds from interviews regardless of who flew first.[20][83] In August 1959, they and their wives signed a contract with Life magazine for $500,000 (equivalent to $4,300,000 in 2018) in exchange for exclusive access to their private lives, homes, and families.[83][27] Their official spokesman from 1959 to 1963 was NASA's public affairs officer, USAF Lieutenant Colonel John "Shorty" Powers, who as a result became known in the press as the "eighth astronaut".[84]

The four surviving Mercury 7 astronauts at a reception after Shepard's memorial service in 1998. Left to right: Glenn, Schirra, Cooper and Carpenter.

As additional groups of astronauts were selected in the 1960s, the Mercury Seven remained in control of management decisions. The Astronaut Office, which was headed by Shepard, was one of three divisions in the Directorate of Flight Crew Operations, which was headed by Slayton. Since twenty-six of the first thirty astronauts were military personnel, the Astronaut Office had a military character, although few of the astronauts wore their uniforms even as much as once a year.[85] There was a bi-weekly military-style pilots' meeting at which activities planned for the upcoming two weeks would be discussed.[86] A "captain's mast" was held afterwards to adjudicate disputes.[87] Shepard ran the Astronaut Office on a "rank has it privileges" basis.[85] The Mercury and 1962 astronauts had their own allocated parking spaces outside Building 4 at Johnson Space Center, while astronauts from later groups had to compete for the remaining spaces allotted to astronauts.[87] While Shepard prohibited junior astronauts from receiving gifts and consulting or teaching part-time, he remained vice president and part owner of the Baytown National Bank in Houston, and devoted much of his time to it.[88] Training was always ungraded; the Mercury astronauts had nothing to gain and much to lose from being objectively compared to the newer classes, as it could threaten their privileged status, managerial control, and priority for flight assignments. The astronaut's attendance at their training events was voluntary.[85] The character of the Astronaut Office would only change after Mercury astronauts retired in the 1970s, and control passed to George Abbey.[72]